Spatial light modulators with light blocking/absorbing areas

ABSTRACT

A projection system, a spatial light modulator, and a method for forming a micromirror array such as for a projection display are disclosed. The spatial light modulator can have two substrates bonded together with one of the substrates comprising a micro-mirror array. The two substrates can be bonded at the wafer level after depositing a getter material and/or solid or liquid lubricant on one or both of the wafers if desired. In one embodiment of the invention, one of the substrates is a light transmissive substrate and a light absorbing layer is provided on the light transmissive substrate to selectively block light from passing through the substrate. The light absorbing layer can form a pattern, such as a frame around an array of micro-mirrors.

TECHNICAL FIELD OF THE INVENTION

[0001] The invention is related generally to spatial light modulators,and, more particularly, to spatial light modulators with light absorbingareas that reduce light from passing through a light transmissivesubstrate—such as around the periphery of an array of pixels in aspatial light modulator.

BACKGROUND OF THE INVENTION

[0002] Spatial Light Modulators (SLMs) are transducers that modulate anincident beam of light in a spatial pattern that corresponds to anoptical or electrical input. A type of SLM is the SLM based on MicroElectro-Mechanical Systems (MEMS). A typical MEMS-based SLM consists ofan array of micro-mirrors mounted on movable elements. Each individualmicro-mirror can be independently deflected by an electrostatic force.Reflection of a beam of incident light impinging a micro-mirror can thenbe controlled, for example by deflecting the micro-mirror throughchanging the electrostatic force applied to the micro-mirror. MEMS-basedSLMs have experienced significant developments and been innovativelyimplemented in many applications, one of which is the use in digitaldisplay systems. In a display application, each micro-mirror isassociated with a pixel of a displayed image. To produce a bright pixel,the state of the micro-mirror associated with the pixel is set in such away that the reflected light from the micro-mirror is directed onto atarget for viewing. And to produce a dark pixel, the status of themicro-mirror is tuned such that the reflected light from themicro-mirror is directed away from the display device. In order todisplay a black-and-white image, the micro-mirror array is illuminatedby a beam of light. By coordinating the reflective status of themicro-mirrors based on the brightness of the pixels of the desiredimage, the collective effect of all reflected lights from individualmicromirrors is the generation of the desired image. Gray-scaled andcolored-images can also be displayed using the micro-mirror array withthe pulse-width-modulation and sequential-color-display techniques,which will not be discussed in detail herein.

[0003] Currently, varieties of MEMS-based SLMs have been developed.Regardless of the differences, the function of the MEMS-based SLMs fordisplay is based on the reflection of light from individualmicro-mirrors. Therefore, the quality of the displayed image stronglydepends on the reflections of the micro-mirrors.

[0004] There are many things that define the quality of a displayedimage. Contrast ratio is a major determinant of perceived image quality.Contrast ratio is the ratio of luminance between the brightest whitethat can be produced and the darkest black that can be produced. If adisplayed image has high contrast ratio, a viewer will judge it to besharper than a displayed image with lower contrast ratio, even if thelower contrast image has substantially more measurable resolution.Contrast ratio of a displayed image from a MEMS-based SLM can beseriously degraded by light scattered, for example, from the edges ofthe micro-mirrors and the structures below the micro-mirrors. Thisscattered light typically travels through the projection lens of thedisplay device and is directed on to the target, even when themicro-mirrors are set for displaying a dark pixel.

[0005] Therefore, methods for use in MEMS-based SLMs are needed toimprove the display quality.

SUMMARY OF THE INVENTION

[0006] In view of the forgoing, the present invention provides a spatiallight modulator with light absorbing areas for improving displayquality. In one embodiment of the invention, the light absorbing areasare disposed so as to decrease light that enters between gaps betweenmicromirrors in the spatial light modulator. In one embodiment of theinvention, a method for making a spatial light modulator is provided,comprising providing a first substrate that is transmissive to visiblelight; providing a second substrate having an array of circuitry andelectrodes thereon; depositing a light absorbing layer on the firstsubstrate to selectively block the passage of light through the firstsubstrate; forming an array of deflectable reflective elements on thefirst or second substrate; and positioning the first and secondsubstrates proximate to each other to form a substrate assembly.

[0007] In another embodiment of the invention, a spatial light modulatoris provided, comprising a first substrate that is transmissive tovisible light; a second substrate having an array of circuitry andelectrodes thereon; a light absorbing layer on the first substratedisposed to selectively block the passage of light through the firstsubstrate; and an array of deflectable reflective elements on the firstor second substrate; wherein the first and second substrates arepositioned proximate to each other as a substrate assembly.

[0008] In a further embodiment of the invention, a projection system isprovided, comprising a light source; a spatial light modulator forreflecting a beam of light from the light source; and projection opticsfor projecting light reflected off of the spatial light modulator;wherein the spatial light modulator comprises: a first substrate that istransmissive to visible light; a second substrate having an array ofcircuitry and electrodes thereon; a light absorbing layer on the firstsubstrate disposed to selectively block the passage of light through thefirst substrate; and an array of deflectable reflective elements on thefirst or second substrate; wherein the first and second substrates arepositioned proximate to each other as a substrate assembly.

[0009] In another aspect of the invention, a spatial light modulator,comprises a first substrate and a second substrate; an array ofcircuitry and electrodes on the second substrate; an opaque layer thatforms a pattern on the first substrate in order to absorb at least 50%of the light that is incident on the opaque layer; and an array ofdeflectable reflective elements on the first or second substrate;wherein the first and second substrates are positioned proximate to eachother as a substrate assembly.

[0010] In still a further example of the invention, a spatial lightmodulator is provided comprising: a first substrate and a secondsubstrate disposed proximate to each other; circuitry, electrodes andmicromirrors formed on the second substrate; and wherein the firstsubstrate is a substrate transmissive to visible light and is disposedat a distance from the first substrate of 75 microns or less. Also aprojection system is disclosed having such a spatial light modulator, alight source and projection optics.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] While the appended claims set forth the features of the presentinvention with particularity, the invention, together with its objectsand advantages, may be best understood from the following detaileddescription taken in conjunction with the accompanying drawings ofwhich:

[0012]FIGS. 1A to 1E are cross-sectional views illustrating one methodfor forming micro-mirrors;

[0013]FIG. 2 is a top view of a micro-mirror showing line 1-1 for thecross-sectional views in FIGS. 1A to 1E;

[0014]FIGS. 3A to 3E are cross-sectional views illustrating the samemethod as in FIGS. 1A to 1E but along a different cross-section;

[0015]FIG. 4 is a top view of a mirror showing line 2-2 for thecross-section of FIGS. 3A to 3E;

[0016]FIG. 5 is an isometric view of the assembly of two substrates, onewith micromirrors, the other with circuitry and electrodes;

[0017]FIG. 6 is a cross-sectional view of the assembled device in use;

[0018]FIG. 7 is a flow chart of one method of the invention;

[0019]FIG. 8 is a top view of a wafer substrate having multiple dieareas;

[0020]FIGS. 9A to 9G are step-by-step views of the assembly of thedevice;

[0021]FIGS. 10A and 10B are top views of two wafers that will be joinedtogether and then singularized;

[0022]FIGS. 10C and 10D are views of light transmissive substrates (FIG.10A) for bonding to a wafer (10D);

[0023]FIG. 11A is a cross-sectional view taken along line 11-11 of FIG.10 upon alignment of the two wafers of FIGS. 10A and 10B, but prior tobonding;

[0024]FIG. 11B is a cross-sectional view taken along line 11-11 of FIG.10 upon alignment of the two wafers of FIGS. 10A and 10B after bondingthe two wafers, but prior to singulation;

[0025]FIG. 12 is an isometric view of a singularized wafer assembly dieheld on a package substrate;

[0026]FIG. 13 is an illustration of a projection system having amicro-mirror device therein;

[0027]FIG. 14A is an illustration of a light absorbing matrix layer onthe light transmissive substrate;

[0028]FIG. 14B is an illustration of another embodiment of a lightabsorbing matrix layer on the light transmissive substrate;

[0029]FIG. 15 is an illustration of light absorbing die frames on alight transmissive substrate;

[0030]FIGS. 16A to 16F are illustrations of light absorbing edges formedalong micro-mirror elements;

[0031]FIG. 17 is an illustration of a light absorbing grid or matrix ona light transmissive substrate with micro-mirrors on an adjacent circuitsubstrate; and

[0032]FIG. 18A and 18B are illustrations of light absorbing areas formedon the wafer with circuitry thereon, wherein FIG. 18A demonstratesabsorbing areas formed on the electrodes; and wherein FIG. 18Bdemonstrates absorbing areas between adjacent electrodes.

DETAILED DESCRIPTION OF THE INVENTION

[0033] Mirror Fabrication:

[0034] Processes for fabricating a MEMS device such as a movablemicro-mirror and mirror array are disclosed in U.S. Pat. Nos. 5,835,256and 6,046,840 both to Huibers, the subject matter of each beingincorporated herein by reference. A similar process for forming MEMSmovable elements (e.g. mirrors) on a wafer substrate (e.g. a lighttransmissive substrate or a substrate comprising CMOS or othercircuitry) is illustrated in FIGS. 1 to 4. By “light transmissive”, itis meant that the material will be transmissive to light at least inoperation of the device (The material could temporarily have a lightabsorbing layer on it to improve the ability to handle the substrateduring manufacture, or a partial light absorbing layer for decreasinglight scatter during use. Regardless, a portion of the substrate, forvisible light applications, is preferably transmissive to visible lightduring use so that light can pass into the device, be reflected by themirrors, and pass back out of the device. Of course, not all embodimentswill use a light transmissive substrate). By “wafer” it is meant anysubstrate on which multiple micro-mirrors or microstructure arrays areto be formed, which allows for being divided into dies, each die havingone or more micro-mirrors thereon. Though not in every situation, ofteneach die is one device or product to be packaged and sold separately.Forming multiple “products” or dies on a larger substrate or waferallows for lower and faster manufacturing costs as compared to formingeach die separately. Of course the wafers can be any size or shape,though it is preferred that the wafers be the conventional rounds orsubstantially round wafers (e.g. 4″, 6″ or 12″ in diameter) so as toallow for manufacture in a standard foundry.

[0035]FIGS. 1A to 1E show a manufacturing process for a micro-mirrorstructure. As can be seen in FIG. 1A, a substrate such as glass (e.g.1737F), quartz, Pyrex™, sapphire, (or silicon alone or with circuitrythereon) etc. is provided. The cross-section of FIGS. 1A-E is takenalong line 1-1 of FIG. 2. Because this cross-section is taken along thehinge of the movable element, an optional block layer 12 can be providedto block light (incident through the light transmissive substrate duringuse) from reflecting off the hinge (or other underlying structure) andpotentially causing diffraction and lowering the contrast ratio (if thesubstrate is transparent). This light-absorbing layer will be describedin more detail in FIG. 14 to FIG. 17.

[0036] As shown in FIG. 1B, a sacrificial layer 14, such as amorphoussilicon, is deposited. The thickness of the sacrificial layer can bewide ranging depending upon the movable element/mirror size and desiredtilt angle, though a thickness of from 500 Å to 50,000 Å, preferablyaround 5000 Å is preferred. Alternatively, the sacrificial layer couldbe a polymer or polyimide (or even polysilicon, silicon nitride, silicondioxide, etc. depending upon the materials selected to be resistant tothe etchant, and the etchant selected). A lithography step followed by asacrificial layer etch form holes 16 a and 16 b in the sacrificialsilicon, which can be of any suitable size, though preferably having adiameter of from 0.1 to 1.5 um, preferably around 0.7±0.25 um. Theetching is performed down to the glass/quartz substrate or down to theblock layer if present. Preferably if the glass/quartz layer is etched,it is in an amount less than 2000 Å.

[0037] At this point, as shown in FIG. 1C, a first layer 18 is depositedby chemical vapor deposition. The material can be any suitable material,for example silicon nitride or silicon oxide deposited by LPCVD orPECVD—however polysilicon, silicon carbide (or other ceramic thin film)or an organic compound could be deposited at this point—or Al, CoSiNx,TiSiNx, TaSiNx and other ternary and higher order compounds as set forthin U.S. patent application Ser. No. 09/910,537 filed Jul. 20, 2001, and60/300,533 filed Jun. 22, 2001 both to Reid and incorporated herein byreference (of course the sacrificial layer and etchant should be adaptedto the material used). Also, laminate structures having variouscombinations of metals (or metal alloys) and ceramic films could bedeposited. The thickness of this first layer can vary depending upon themovable element size and desired amount of stiffness of the element.However in one embodiment the layer has a thickness of from 100 to 3200Å, more preferably around 1100 Å. The first layer undergoes lithographyand etching so as to form gaps between adjacent movable elements on theorder of from 0.1 to 25 um, preferably around 1 to 2 um.

[0038] A second layer 20 (the “hinge” layer) is deposited as shown inFIG. 1D. By “hinge layer” it is meant the layer that defines thatportion of the device that flexes to allow movement of the device. Thehinge layer can be disposed only for defining the hinge, or for definingthe hinge and other areas such as the mirror. In any case, thereinforcing material is removed prior to depositing the hinge material.The material for the second (hinge) layer can be the same (e.g. siliconnitride) as the first layer or different (e.g. any suitable materialsuch as silicon oxide, silicon carbide, polysilicon, or Al, CoSiNx,TiSiNx, TaSiNx or other ternary and higher compounds) and can bedeposited by chemical vapor deposition like the first layer. Thethickness of the second/hinge layer can be greater or less than thefirst, depending upon the stiffness of the movable element, theflexibility of the hinge desired, the material used, etc. In oneembodiment the second layer has a thickness of from 50 Å to 2100 Å,preferably around 500 Å. In another embodiment, the first layer isdeposited by PECVD and the second layer by LPCVD.

[0039] As also shown in FIG. 1D, a reflective and conductive layer 22 isdeposited. The reflective/conductive material can be gold, aluminum orother metal, or an alloy of more than one metal though it is preferablyaluminum deposited by PVD. The thickness of the metal layer can be from50 to 2000 Å, preferably around 500 Å. It is also possible to depositseparate reflective and conductive layers. An optional metal passivationlayer (not shown) can be added, e.g. a 10 to 1100 Å silicon oxide layerdeposited by PECVD. Then, photoresist patterning on the metal layer isfollowed by etching through the metal layer with a suitable metaletchant. In the case of an aluminum layer, a chlorine (or bromine)chemistry can be used (e.g. a plasma/RIE etch with Cl₂ and/or BCl₃ (orC12, CC14, Br2, CBr₄, etc.) with an optional preferably inert diluentsuch as Ar and/or He)., The sacrificial layer is then removed in orderto “release” the micro-mirror structures (FIG. 1E).

[0040] In the embodiment illustrated in FIGS. 1A to 1E, both the firstand second layers are deposited in the area defining the movable(mirror) element, whereas the second layer, in the absence of the firstlayer, is deposited in the area of the hinge. It is also possible to usemore than two layers to produce a laminate movable element, which can bedesirable particularly when the size of the movable element is increasedsuch as for switching light beams in an optical switch. A plurality oflayers could be provided in place of a single layer 18 in FIG. 1C, and aplurality of layers could be provided in place of layer 20 and in placeof layer 22. Or, layers 20 and 22 could be a single layer, e.g. a puremetal layer or a metal alloy layer or a layer that is a mixture of e.g.a dielectric or semiconductor and a metal. Some materials for such layeror layers that could comprise of metal alloys and dielectrics orcompounds of metals and nitrogen, oxygen or carbon (particularly thetransition metals) are disclosed in U.S. provisional patent application60/228,007, the subject matter of which is incorporated herein byreference.

[0041] In one embodiment, the reinforcing layer is removed in the areaof the hinge, followed by depositing the hinge layer and patterning bothreinforcing and hinge layer together. This joint patterning of thereinforcing layer and hinge layer can be done with the same etchant(e.g. if the two layers are of the same material) or consecutively withdifferent etchants. The reinforcing and hinge layers can be etched witha chlorine chemistry or a fluorine (or other halide) chemistry (e.g. aplasma/RIE etch with F₂, CF₄, CHF₃, C₃F₈, CH₂F₂, C₂F₆, SF₆, etc. or morelikely combinations of the above or with additional gases, such asCF₄/H₂, SF₆/Cl₂, or gases using more than one etching species such asCF₂Cl₂, all possibly with one or more optional inert diluents). Ofcourse, if different materials are used for the reinforcing layer andthe hinge layer, then a different etchant can be employed for etchingeach layer. Alternatively, the reflective layer can be deposited beforethe first (reinforcing) and/or second (hinge) layer. Whether depositedprior to the hinge material or prior to both the hinge material and thereinforcing material, it is preferable that the metal be patterned (e.g.removed in the hinge area) prior to depositing and patterning the hingematerial.

[0042]FIGS. 3A to 3E illustrate the same process taken along a differentcross-section (cross-section 2-2 in FIG. 4) and show the optional blocklayer 12 deposited on the light transmissive substrate 10, followed bythe sacrificial layer 14, layers 18, 20 and the metal layer 22. Thecross-sections in FIGS. 1A to 1E and 3A to 3E are taken alongsubstantially square mirrors in FIGS. 2 and 4 respectively. However, themirrors need not be square but can have other shapes that may decreasediffraction and increase the contrast ratio. Such mirrors are disclosedin U.S. provisional patent application 60/229,246 to Ilkov et al., thesubject matter of which is incorporated herein by reference. The lightabsorbing material on the light transmissive substrate, as will bediscussed below, can be made to conform to the shape of themirrors—whether the mirrors are formed on the light transmissivesubstrate or on a semiconductor substrate having circuitry, electrodesand micro-mirrors thereon. Also, the mirror hinges can be torsion hingesas illustrated in this provisional application.

[0043] It should also be noted that materials and method mentioned aboveare examples only, as many other method and materials could be used. Forexample, the Sandia SUMMiT process (using polysilicon for structurallayers) or the Cronos MUMPS process (also polysilicon for structurallayers) could be used in the present invention. Also, a MOSIS process(AMI ABN—1.5 um CMOS process) could be adapted for the presentinvention, as could a MUSiC process (using polycrystalline SiC for thestructural layers) as disclosed, for example, in Mehregany et al., ThinSolid Films, v. 355-356, pp. 518-524, 1999. Any suitable deposition andpatterning methods can be used, depending upon the structure desired tobe deposited. Also, the sacrificial layer and release etchant disclosedherein are exemplary only. For example, a silicon dioxide sacrificiallayer could be used and removed with HF (or HF/HCI), or a siliconsacrificial could be removed with CIF3 or BrF3. Also a PSG sacrificiallayer could be removed with buffered HF, or an organic sacrificial suchas polyimide could be removed in a dry plasma oxygen release step. Ofcourse the release etchant and sacrificial material should be selecteddepending upon the structural material to be used. Also, though PVD andCVD are referred to above, other thin film deposition methods could beused for depositing the layers, including spin-on, sputtering,anodization, oxidation, electroplating and evaporation.

[0044] After forming the micro-mirrors as in FIGS. 1 to 4 on the firstwafer, it is preferable to remove the sacrificial layer so as to releasethe micro-mirrors. This release can be performed at the die level,though it is preferred to perform the release at the wafer level. FIGS.1E and 3E show the micro-mirrors in their released state. As can be seenin FIG. 1E, posts 24 hold the released microstructure on substrate 10.

[0045] Also, though the hinge of each mirror can be formed in the sameplane as the mirror element (and/or formed as part of the samedeposition step) as set forth above, they can also be formed separatedfrom and parallel to the mirror element in a different plane and as partof a separate processing step. This superimposed type of hinge isdisclosed in FIGS. 11 and 12 of the previously-mentioned U.S. Pat. No.6,046,840, and in more detail in U.S. patent application Ser. No.09/631,536 to Huibers et al. filed Aug. 3, 2000, the subject matter ofwhich being incorporated herein by reference. Whether formed with onesacrificial layer as in the figures, or two (or more) sacrificial layersas for the superimposed hinge, such sacrificial layers are removed aswill be discussed below, with a preferably isotropic etchant. This“release” of the mirrors can be performed immediately following theabove described steps, or after shipment from the foundry at the placeof assembly.

[0046] In one embodiment the resolution is XGA, 1024×768 pixels, thoughother resolutions are possible. A pixel pitch of from 5 to 24 um ispreferred (e.g. 14 um).

[0047] Backplane:

[0048] The second or “lower” substrate (the backplane) die contains alarge array of electrodes on the top metal layer of the die. Eachelectrode electrostatically controls one pixel (one micro-mirror on theupper optically transmissive substrate) of the microdisplay. The voltageon each electrode on the surface of the backplane determines whether itscorresponding microdisplay pixel is optically ‘on’ or ‘off,’ forming avisible image on the microdisplay. Details of the backplane and methodsfor producing a pulse-width-modulated grayscale or color image aredisclosed in U.S. patent application Ser. No. 09/564,069 to Richards,the subject matter of which is incorporated herein by reference. Ofcourse a wide variety of methods for causing actuation of themicro-mirrors are available.

[0049] In a preferred embodiment, the display pixels themselves arepreferably binary, always either fully ‘on’ or fully ‘off,’ and so thebackplane design is purely digital. The number of reflective elements(display pixels) in each die can be any number, such as from 6,000 toabout 6 million, depending upon the desired resolution of the display.Though the micro-mirrors could be operated in analog mode, no analogcapability is necessary. For ease of system design, the backplane's I/Oand control logic preferably run at a voltage compatible with standardlogic levels, e.g. 5V or 3.3V. To maximize the voltage available todrive the pixels, the backplane's array circuitry may run from aseparate supply, preferably at a higher voltage.

[0050] One embodiment of the backplane can be fabricated in a foundry 5Vlogic process. The mirror electrodes can run at 0-5V or as high above 5Vas reliability allows. The backplane could also be fabricated in ahigher-voltage process such as a foundry Flash memory process using thatprocess's high-voltage devices. The backplane could also be constructedin a high-voltage process with larger-geometry transistors capable ofoperating at 12V or more. A higher voltage backplane can produce anelectrode voltage swing significantly higher than the 5-7V that thelower voltage backplane provides, and thus actuate the pixels morerobustly.

[0051] In digital mode, it is possible to set each electrode to eitherstate (on/off), and have that state persist until the state of theelectrode is changed. A RAM-like structure, with one bit per pixel is anarchitecture that can accomplish this. One example is an SRAM-basedpixel cell. Alternate well-known storage elements such as latches orDRAM (pass transistor plus capacitor) are also possible. If a dynamicstorage element (e.g. a DRAM-like cell) is used, it is desirable that itbe shielded from incident light that might otherwise cause leakage.

[0052] A grayscale or full-color image can be produced by modulatingpixels rapidly on and off, for example according to the method in theabove-mentioned U.S. patent application Ser. No. 09/564,069 to Richardsor other suitable methods. In order to support this, it is preferablethat the backplane allows the array to be written in random-accessfashion, though finer granularity than a row-at-a-time is generally notnecessary.

[0053] It is desirable to minimize power consumption, primarily forthermal reasons. Decreasing electrical power dissipation will increasethe optical/thermal power budget, allowing the microdisplay to toleratethe heat of more powerful lamps. Also, depending upon the way themicrodisplay is assembled (wafer-to-wafer join+offset saw), it may bepreferable for all I/O pads to be on one side of the die. To minimizethe cost of the finished device it is desirable to minimize pin count.For example, multiplexing row addresses or other infrequently-usedcontrol signals onto the data bus can eliminate separate pins for thesefunctions with negligible throughput penalties (a few percent, e.g. oneclock cycle for address information per row of data is acceptable). Adata bus, a clock, and a small number of control signals (5 or less) areall that is necessary.

[0054] In use, the die can be illuminated with a 200 W or more arc lamp.The thermal and photo-carrier effects of this may result in speciallayout efforts to make the metal layers as ‘opaque’ as possible over theactive circuitry to reflect incident optical energy and minimizephotocarrier and thermal effects. Also, some light can get between themirrors or hit the mirror edges, and then scatter from one or moresurfaces and end up entering the projection lens/collection optics whenthe dark state is desired. This has the negative effect of reducingcontrast.

[0055] To eliminate this scattered light non-reflective material can beplaced on the backplane as a final layer. The non-reflective materialcan be a dark, opaque (e.g. black, grey or other dark color) thin film.Examples of materials that can be placed on backplane to absorbscattered light include a non-conductive blanket film such as polyimidewith carbon particles (e.g. DARC (TM) from Brewer Science). Or otherdark colored ceramic films such as CrN, TiAIN, TaN or other filmscomprising of carbon, such as amorphous CN, amorphous CAIN, TiCN, a-DLC,SiC, TiAICN, WC, etc.—preferably a non-conductive film can be used. Inthe alternative, conductive dark films could be used that are placeddirectly over the electrodes on the backplane and are electricallyconnected to the electrodes. Such a film could be a dark metal or metalalloy such as sputtered black chrome or niobium that has a reflectanceas low as 3%. The black chrome coating can be a multilayer structure ofchrome and chromium oxide (to match the index of refraction, as in anantireflective coating laminate). Of course, other opaque films(preferably those with high optical density, thermally stable and withlow reflectivity) can be deposited and patterned (the opacity and colorof many films being variable due to deposition parameters). Lightabsorbing conductive materials that can be deposited on the electrodesinclude black nickel, and films comprising carbon, such as a-DLC orvitreous carbon. It is also possible to deposit a dark conductive gridor matrix surrounding all of the electrodes (without electricallyconnecting the electrodes).

[0056] It is also possible to put an “anti-reflective coating” (an ARfilm) on the backplane. For example a normally absorptive surface canhave enhanced absorption if an “AR film” stack (for example lighttransmissive dielectric layers), are placed above it so that lightreflection is reduced due to destructive interference. Such dielectricslayers can be designed to work particularly well at certain wavelengthsand/or angles—and can be used for the matrix or frame on the lighttransmissive substrate, as will be discussed below.

[0057] Assembly

[0058] After the upper and lower substrates (wafers) are finished beingprocessed (e.g. circuitry/electrodes on lower wafer, micro-mirrors onupper wafer), the upper and lower wafers are joined together. Thisjoining of the two substrates allows micro-mirrors on one substrate tobe positioned proximate to electrodes on the other substrate. Thisarrangement is illustrated in FIGS. 5 and 6, which will be describedfurther below.

[0059] The method for the assembly of the wafers and separation of thewafer assembly into individual dies is similar to the method forassembly of liquid crystal devices as disclosed in U.S. Pat. No.5,963,289 to Stefanov et al, “Asymmetrical Scribe and Separation Methodof Manufacturing Liquid Crystal Devices on Silicon Wafers”, which ishereby incorporated by reference. Many bonding methods are possible suchas adhesive bonding (e.g. epoxy, silicone, low K material or otheradhesive—described further herein), anodic bonding, compression bonding(e.g. with gold or indium) metal eutectic bonding, solder bonding,fusion bonding, or other wafer bonding processes known in the art.Whether the upper and lower wafer are made of the same or differentmaterials (silicon, glass, dielectric, multilayer wafer, etc.), they canfirst be inspected (step 30 in the flow chart of FIG. 7) for visualdefects, scratches, particles, etc. After inspection, the wafers can beprocessed through industry standard cleaning processes (step 32 in theflow chart of FIG. 7). These include scrubbing, brushing or ultrasoniccleaning in a solvent, surfactant solution, and/or de-ionized (DI)water.

[0060] The mirrors are preferably released at this point (step 34 in theflow chart of FIG. 7). Releasing immediately prior to the application ofepoxy or bonding is preferable (except for an optional stictiontreatment between release and bonding). For silicon sacrificial layers,the release can be in an atmosphere of xenon difluoride and an optionaldiluent (e.g. nitrogen and/or helium). Of course, other etchants couldbe used, including interhalogens such as bromine trifluoride and brominetrichloride. The release is preferably a spontaneous chemical etch whichdoes not require plasma or other external energy to etch the siliconsacrificial layer(s). Or the release can be performed with asupercritical fluid such as set forth in U.S. patent application Ser.No. 10/167,272 filed Jun. 10, 2002, incorporated herein by reference.After etching, the remainder of the device is treated for stiction (step36 in the flow chart of FIG. 7) by applying an anti-stiction layer (e.g.a self assembled monolayer). The layer is preferably formed by placingthe device in a liquid or gas silane, preferably a halosilane, and mostpreferably a chlorosilane. Of course, many different silanes are knownin the art for their ability to provide anti-stiction for MEMSstructures, including the various trichlorsilanes set forth in “SelfAssembled Monolayers as Anti-Stiction Coatings for MEMS: Characteristicsand Recent Developments”, Maboudian et al., as well as otherunfluorinated (or partially or fully fluorinated) alkyltrichlorosilanes, preferably those with a carbon chain of at least 10carbons, and preferably partially or fully fluorinated.(Tridecafluoro-1,1,2,2-tetrahydro-octyl)trichlorosilane available fromGelest, Inc. is one example. Other trichlorosilanes (preferablyfluorinated) such as those with phenyl or other organic groups having aring structure are also possible.

[0061] In order to bond the two wafers together, spacers are mixed intosealant material (step 38 in the flow chart of FIG. 7). Spacers in theform of spheres or rods are typically dispensed and dispersed betweenthe wafers to provide cell gap uniformity and space for mirrordeflection. Spacers can be dispensed in the gasket area of the displayand therefore mixed into the gasket seal material prior to sealdispensing. This is achieved through normal agitated mixing processes.The final target for the gap between the upper and lower wafers ispreferably from 1 to 10 um, though other gaps are possible dependingupon factors such as micro-mirror size and deflection angle. The spheresor rods can be made of glass or plastic, preferably an elasticallydeforming material. Alternatively, spacer pillars can be fabricated onat least one of the substrates. In one embodiment, pillars/spacers areprovided only at the side of the array. In another embodiment,pillars/spacers can be fabricated in the array itself. Other bondingagents with or without spacers could be used, including anodic bondingor metal compression bonding with a patterned eutectic or metal.

[0062] A gasket seal material can then be dispensed (step 40 in the flowchart of FIG. 7) on the bottom substrate in a desired pattern, usuallyin one of two industry standard methods including automated controlledliquid dispensing through a syringe and printing (screen, offset, orroller). When using a syringe, it can be moved along X-Y coordinatesrelative to the parts. The syringe tip is constrained to be just abovethe part with the gasket material forced through the needle by positivepressure. Positive pressure can be provided either by a mechanicalplunger forced by a gear driven configuration and/or by an air pistonand/or pressed through the use of an auger. Of course many differentadhesive dispensing methods can be used.

[0063] Then, the two wafers are aligned (step 42 in the flow chart ofFIG. 7) preferably to within 1 micron accuracy or less. Alignment of theopposing electrodes or active viewing areas is aided by registration ofsubstrate fiducials on opposite substrates. This task can beaccomplished with the aid of video cameras with lens magnification. Themachines range in complexity from manual to fully automated with patternrecognition capability. Whatever the level of sophistication, theypreferably accomplish the following: (a) Dispense a very small amount ofa UV curable adhesive at locations near the perimeter and off of allfunctional devices in the array; (b) Align the fiducials of the opposingsubstrates within the equipment capability; and (c) Press substrates andUV tack for fixing the wafer-to-wafer alignment through the remainingbonding process (e.g., curing of the internal epoxy).

[0064] The final cell gap can be set by pressing (step 44 in the flowchart of FIG. 7) the previously tacked laminates in a UV or thermalpress. In a UV press, a common procedure would have the substratesloaded into a press where at least one or both of the press platens arequartz, in order to allow UV radiation from a UV lamp to pass unabatedto the gasket seal epoxy. Exposure time and flux rates are processparameters determined by the equipment and adhesive materials. Thermallycured epoxies require that the top and bottom platens of a thermal pressbe heated. The force that can be generated between the press platens istypically many pounds. With thermally cured epoxies, after the initialpress the arrays are typically transferred to a stacked press fixturewhere they can continually to be pressed and post-cured for 4-8 hours.

[0065] Once the wafers have been bonded together to form a waferassembly, the assembly can be separated into individual dies (step 46 inthe flow chart of FIG. 7). Silicon substrate and glass scribes areplaced on the respective substrates in an offset relationship at leastalong one direction. Or, the substrates can be provided initially withscribes on them already. The units are then separated, resulting in eachunit having a bond pad ledge on one side and a glass electrical contactledge on an opposite side—if such an offset arrangement is desired. Theparts may be separated from the array by any of the following methods.The order in which the array (glass first) substrate is scribed isimportant when conventional solid-state cameras are used for viewing andalignment in a scribe machine. This constraint exists unless specialinfrared viewing cameras are installed which make the silicontransparent and therefore permits viewing of front surface metalfiducials. The scribe tool is aligned with the scribe fiducials andprocessed. The resultant scribe lines in the glass can be used asreference marks to align the silicon substrate scribe lanes. Thesescribe lanes may be coincident with the glass substrate scribes oruniformly offset. The parts are then separated from the array by ventingthe scribes on both substrates. Automatic breaking is done bycommercially available guillotine or fulcrum breaking machines. Theparts can also be separated by hand. Or, any other suitablesingularization method can be used to separate the bonded wafers intobonded wafer die portions.

[0066] For example, separation may also be done by glass scribing andpartial sawing of the silicon substrate. Sawing requires an additionalstep at gasket dispense. Sawing can be performed in the presence of ahigh-pressure jet of water. Moisture should preferably not be allowed inthe area of the fill port or damage of the MEMS structures could occur.Therefore, at gasket dispense, an additional gasket bead must bedispensed around the perimeter of the wafer. The end of each scribe/sawlane must be initially left open, to let air vent during the align andpress processes. After the array has been pressed and the gasketmaterial cured, the vents are then closed using either the gasket orend-seal material. The glass is then aligned and scribed as describedabove. Sawing of the wafer is done from the backside of the siliconwhere the saw streets are aligned relative to the glass scribe lanesdescribed above. The wafer is then sawed to a depth of 50%-90% of itsthickness. The parts are then separated as described above.

[0067] Alternatively, both the glass and silicon substrates may bepartially sawed prior to part separation. With the same gasket sealconfiguration, vent and seal processes as described above, saw lanes arealigned to fiducials on the glass substrates. The glass is sawed to adepth between 50% and 95% of its thickness. The silicon substrate issawed and the parts separated as described above.

[0068] For an illustrated example of the above, reference is made toFIG. 8 where 45 die areas have been formed on wafer 5. Each die area 3(having a length A and a height B) comprises one or more (preferablyreleased) micro-mirrors. In the case of micro-mirror arrays forprojection systems, each die preferably has at least 1000 movablemirrors, and more likely between 1 and 6 million movable elements.

[0069] As can be seen in FIG. 9A, four die areas 3 a to 3 d are formedon wafer 5 (many more dies would be formed in most circumstances, thoughonly four are shown for ease of illustration). Each die area 3 a to 3 dcomprises one or more micro-mirrors, which have already been released ina suitable etchant. As illustrated in FIG. 9B, epoxy can be applied inthe form of beads 51 a to 51 d along each side of the die area, or asbeads 53 a to 53 d at each corner of the die area. Or, epoxy ribbons 55a and 55 b could be applied along two sides of each die, or a singleribbon 57 could be applied substantially surrounding an entire die. Ofcourse many other configurations are possible, though it is desirablethat the die not be fully surrounded with an epoxy gasket, as this willprevent air or other gas from escaping when the two wafers are pressedtogether during a full or partial epoxy cure. And, of course, it ispreferable, for higher manufacturing throughput, to use a common epoxyapplication method throughout the entire wafer (the different types ofapplications in FIG. 9B are for illustrations purposes only). Also, theareas in which epoxy is applied can first have a sacrificial materialdeposited in that area (preferably in an area larger than the bead orband of epoxy due to expansion of the epoxy under compression). Thesacrificial material could also be applied to the entire wafer except inareas having micro-mirrors thereon. Also, a conductive epoxy (or otheradhesive) could be used in order to make electrical contact between thewafer having circuitry and electrodes and the wafer having MEMS thereon.

[0070] In FIG. 9C, upper wafer 25 and the lower substrate wafer 5 withmicromirrors (and optionally circuitry) are brought into contact witheach other. The final gap between the two wafers can be any size thatallows the two wafers to be held together and singularized uniformly.Because gasket beads will expand upon application of pressure (thustaking up valuable real estate on a wafer with densely positioned dieareas), it is preferable that the gap size be larger than 1 um, andpreferably greater than 10 um. The gap size can be regulated byproviding microfabricated spacers or spacers mixed in with the epoxy(e.g. 25 um spacers). However, spacers may not be necessary dependingupon the type of microstructure and the amount of pressure applied.

[0071]FIG. 9D shows the lower wafer 5 and upper wafer 25 bondedtogether. Horizontal and vertical score or partial saw lines 21 a and 21b are provided on both the upper wafer 25 and the first (lower) wafer 5(lines not shown on wafer 5). Preferably the score lines on the twowafers are offset slightly from each other at least in one of the(horizontal or vertical). This offset scoring or partial sawing allowsfor ledges on each die when the wafer is completely singularized intoindividual dies (see FIG. 9E). Electrical connections 4 on ledge 6 ondie 3 c allow for electrical testing of the die.

[0072] Referring again to FIG. 5, a top perspective view of a portion ofa bonded wafer assembly die 10 is illustrated. Of course, the mirrorshapes illustrated in FIGS. 1 to 5 are exemplary, as many other mirrorstructures are possible, such as set forth in U.S. patent applicationSer. No. 09/732,445 to Ilkov et al. filed Dec. 7, 2000, incorporatedherein by reference. For clarity, only four pixel cells 54, 54 a, 54 band 54 c in a two by two grid configuration are shown in FIG. 5. Thepixel cells 54, 54 a, 54 b and 54 c have a pixel pitch of, for example,12 microns. “Pixel pitch” is defined as the distance between likeportions of neighboring pixel cells.

[0073] Reflective deflectable elements (e.g., mirrors 48, 48 a, 48 b and48 c), each corresponding to a respective pixel cell 54, 54 a, 54 b and54 c, are attached to the lower surface 14 of the optically transmissivesubstrate 52 in an undeflected position. Thus, mirrors 48, 48 a, 48 band 48 c are visible through optically transmissive substrate 52 in FIG.5. For clarity, light blocking aperture layers 56 if present, betweenthe mirrors 48, 48 a, 48 b or 48 c and the optically transmissivesubstrate 52, are represented only by dashed lines so as to showunderlying hinges 50, 50 a, 50 b and 50 c. The distance separatingneighboring mirrors may be, for example, 0.5 microns or less.

[0074] The optically transmissive substrate 52 is made of materials,which can withstand subsequent processing temperatures. The opticallytransmissive substrate 52 may be, for example, a 4 inch quartz wafer 500microns thick. Such quartz wafers are widely available from, forexample, Hoya Corporation U.S.A at 960 Rincon Circle, San Jose, Calif.95131. Or, the substrate can be glass such as Coming 1737 or ComingEagle2000 or other suitable optically transmissive substrate. In apreferred embodiment, the substrate is transmissive to visible light,and can be display grade glass.

[0075] As can be seen in FIG. 6, the light transmissive substrate 52 isbonded to e.g. a MOS-type substrate 62 (a semiconductor substrate can beused such as a silicon substrate with circuitry and electrodes formedthereon) in spaced apart relation due to spacers 66. A plurality ofelectrodes 63 are disposed adjacent a plurality of micro-mirrors 64(mirrors simplified and only 9 illustrated for convenience) forelectrostatically deflecting the micromirrors. An incoming light beam 65a will be reflected by a non-deflected mirror at the same angle as it isincident, but will be deflected “vertically” as outgoing light beam 65 bwhen the mirror is deflected. An array of thousands or millions ofmirrors selectively moving and deflecting light “vertically” towardprojection optics, along with a color sequencer (wheel or prism) thatdirects sequential beams of different colors onto the mirrors, resultsin a color image projected on a target (e.g. for projection television,boardroom projectors, etc.). A simplified schematic of one type ofprojection system is illustrated in FIG. 13, where a light source 110,e.g. an arc lamp having a reflector 120, directs light through a colorsequencer (e.g. color wheel 130 that rotates around axis of rotation 170via motor 140), after which the light enters light pipe 150 and optics160 so as to be incident on a micro-mirror array 180 and is reflectedoff of the micro-mirrors of the array and projected via projectionoptics 190 to a target 210.

[0076] The method for forming micro-mirrors as set forth above is butone example of many methods for forming many different MEMS devices(whether with or without an electrical component), in accordance withthe present invention. Though the electrical component of the final MEMSdevice is formed on a separate wafer than the micro-mirrors in the aboveexample, it is also possible to form the circuitry and micro-mirrorsmonolithically on the same substrate. The method for forming suchmicro-mirrors could be similar to the methods described herein (with thedifference being that the mirrors are formed on the substrate afterforming circuitry and electrodes). Or, other methods for formingcircuitry and micro-mirrors monolithically on the same substrate asknown in the art could be used.

[0077]FIGS. 10A and 10B show two wafers that will be joined together andthen singularized. FIG. 10A is a top view of a light transmissive coverwafer (having a mask area, getter area, lubricant area and compressionmetal bonding area) whereas FIG. 10B is an illustration of such amonolithically formed mirror array (e.g. for a spatial light modulator)on a bottom semiconductor wafer (along with a metal area for compressionbonding). Referring first to FIG. 10B, a plurality of mirror arrays 71 ato 71 e is formed on a “bottom” wafer 70 (e.g. a silicon wafer). Afterthe mirrors are released, a metal for compression bonding is applied(areas 73 a to 73 e) around each mirror array. Of course more arrayscould be formed on the wafer (as shown in FIG. 8). On a “top” wafer 80(e.g. glass or quartz—preferably display grade glass) are formed masks81 a-e, which will block visible light around a perimeter area of eachdie from reaching the mirror arrays after the two wafers are bonded andsingularized. Also illustrated in FIG. 10A are areas of lubricant 83a-e, areas of getter material 85 a-e, and areas of metal for compressionbonding 87 a-e. If the wafer of FIG. 10B has been treated with a selfassembled monolayer or other lubricant, then the addition of a lubricanton the wafer of FIG. 10A may be omitted if desired (although multipleapplications of lubricants can be provided). The lubricant applied tothe wafer as a gasket, band or drop on the wafer, can be any suitablelubricant, such as the various liquid or solid organic (or hybridorganic-inorganic materials) as known in the art. In one embodiment, atrichlorosilane SAM is applied to the entire wafer or large portions ofthe wafer at least covering the micro-mirror elements, and a silicone isapplied to the lubricant areas 83 a-e. The metal for compression bondingcould be any suitable metal for this purpose such as gold or indium.(Alternatively, if an adhesive is used, the adhesive could be anysuitable adhesive, such as an epoxy or silicone adhesive, and preferablyan adhesive with low outgassing). Of course any combination of theseelements could be present (or none at all if the bonding method is otherthan an adhesive bonding method). Preferably one or more of the mask,lubricant, getter and bonding material are present on the “top” wafer 80prior to bonding. Also, the lubricant, getter and bonding material couldbe applied to only the top or bottom wafer or both wafers. In analternate embodiment, it may be desirable to apply the lubricant andgetter to the bottom wafer around the circuitry and electrodes, withbonding material on both wafers. Of course, depending upon the MEMSapplication, the mask (or the lubricant or getter) may be omitted (e.g.for non-display applications). Also, the bands of lubricant, getter andbonding material need not fully encircle the “die area” on the wafer,but could be applied in strips of dots as illustrated in FIG. 9B. If thebonding material does not fully encircle the MEMS die area, then, priorto singulation, it is preferred that the bonding material “gap” befilled so as to protect the MEMS devices during singulation (fromparticulate and/or liquid damage depending upon the singulation method).

[0078] It is also possible to bond multiple substrates (smaller than asingle wafer) to another wafer. In the embodiment illustrated in FIGS.10C and 10D, substrates 101 a to 101 d are substrates transmissive tovisible light and have thereon masks 81 a to 81 d as well as areas oflubricant 83 a to 83 d, areas of getter material 85 a to 85 d, and areasof bonding material 87 a to 87 d (e.g. gold or indium for metalcompression bonding. The mask areas are preferably “picture frame”shaped rectangular areas that block the transmission of visible light.This arrangement is desirable for selectively blocking light incident onmicro-mirror arrays formed on the wafer. After bonding the multiplesubstrates with mask areas to the wafer, the wafer is singularized intowafer assembly portions, followed by packaging such as in FIG. 12.

[0079] The MEMS wafers could be made of any suitable material, dependingupon the final application for the devices, including silicon, glass,quartz, alumina, GaAs, etc. Silicon wafers can typically be processed toinclude circuitry. For an optical MEMS application (e.g. micro-mirrorsfor optical switching or for displays), the “top” wafer of FIG. 10A ispreferably transparent, as mentioned above. The mask illustrated in FIG.10A, can be an absorptive or reflective mask, such as one made from TiN,AIN, or other oxide or nitride compound, or polymers or other suitablematerials having sufficient light absorbing capabilities. This “top”wafer could also incorporate other optical elements, such as lenses, UVor other types of filters or antireflection and/or antiscratch coatings.

[0080] Then, the two wafers are aligned, bonded, cured (e.g. with UVlight or heat depending upon the type of adhesive used) and singularizedas set forth above. FIG. 11A is a cross-section taken along line 11-11in FIG. 10A (after alignment with bottom wafer 70 in FIG. 10B), whereasFIG. 10B is the same cross-section after bonding (but beforesingulation). FIG. 12 is an illustration of a packaged wafer assemblyportion after singularization of the bonded wafers. As can be seen inFIG. 12, a lower substrate 94 is bonded to the upper substrate 93, withthe lower substrate held on a lower packaging substrate 90. Metal areas96 on lower wafer portion 94 will be electrically connected to metalareas 97 on the package substrate 90. As can be seen in this Figure,unlike other MEMS packaging configurations, there is no need to furtherencapsulate or package the wafer assembly die formed of substrates 93and 94, as the MEMS elements are already protected within the waferassembly (though a “second” package surrounding the substrate assemblycould be used for added protection and hermeticity). As such, the diecomprised of two-bonded die substrates (light transmissive andsemiconductor, for example, with MEMS elements on the light transmissivesubstrate) seal (preferably hermetically) the MEMS elements fromambient. A micro-mirror array comprised of micro-mirrors held on a firstsubstrate (preferably glass and more preferably display quality glass)which substrate is bonded to a semiconductor substrate (preferablysilicon) which in turn is bonded to a lower package substrate that doesnot fully encapsulate the bonded die substrates (because the lighttransmissive and semiconductor substrates already encapsulate the MEMSelements) is a less expensive alternative to standard packaging ofmicro-mirror arrays for projection displays. Also, such a packagingarrangement allows for providing anti-stiction treatment, getters etc.at the wafer level further decreasing costs of packaging the device. Ofcourse, an additional package surrounding the substrate assembly couldalso be used.

[0081] Alternatively, it is possible to fully encapsulate the two bondeddie substrates within a fully surrounding package (having an opticallytransmissive window for light to enter and exit the package). Such afully surrounding package could be a hermetic package with, for example,a pressure less than ambient pressure. The pressure between the bondeddie substrates hermetically sealed together can be less than 1 atm,preferably less than 0.25 atm, and more preferably less than Torr. Ifvery low pressures are desired, then pressures between the substrates ofless than 10 Torr, less than 1 Torr or even as low as 100 mTorr can beused. Getters, lubricants, etc. could be disposed within thissurrounding package rather than within the bonded substrates.

[0082] As mentioned above in relation to FIGS. 11A and 11B, on the lighttransmissive wafer 80 (e.g. glass or quartz—preferably display gradeglass) are formed masks 81 a to 81 e which will block visible lightaround a perimeter area of each die from reaching the mirror arraysafter the two wafers are bonded and singularized. This “frame” of lightabsorbing material is preferably one that absorbs many wavelengths inthe visible spectrum. An opaque material, preferably a black material ispreferred for the mask around the perimeter of each die. Such frames or“masks” around each micro-mirror array are shown in FIG. 15. In thisfigure, a light transmissive substrate 102 is provided with lightblocking/absorbing frame areas 100 that surround each die area 101 onthe substrate 102. The material that forms the dark frame area 100 canbe thin film deposited by CVD, PVD etc. and patterned to form the frameareas around each die area on the wafer. In one embodiment ion beamsputtered black chrome or niobium is used, that has a reflectance as lowas 3% through the light transmissive substrate, with high thermalstability. After sputtering the film onto e.g. glass, it is etched toform the “frames” in each die area. The black chrome coating can be amultilayer structure of chrome and chromium oxide (to match the index ofrefraction, as in an antireflective coating laminate). Of course, otheropaque films (preferably those with high optical density, thermallystable and with low reflectivity) can be deposited and patterned (theopacity and color of many films being variable due to depositionparameters). Light absorbing materials can be used such as black nickel,CrN, TiAlN, TaN and many films comprising carbon, such as amorphous CN,amorphous CAIN, TiC, TiCN, a-DLC, vitreous carbon, SiC, TiAlCN, WC, etc.Multilayer structures, such as TiC/WC, WC/C or TiAlN/WC/C, can be used,as well as other multilayer structures with matched indices. Alsopolyimides and other polymers containing carbon black (or other opacityincreasing material) can be used. If the light-absorbing layer isexposed to an etchant at the time of release of the micro-mirrors, thelight absorbing material should preferably be resistant to the etchantused.

[0083] Forming the light absorbing areas can be by any suitable filmforming method—such as standard deposition and patterning techniques.For example, the metals and metal alloys can be deposited by sputteringa target in an inert atmosphere. Other techniques, such aselectroplating can be used. For ceramic materials, a target can bereactively sputtered such as in a nitrogen atmosphere to form nitrideceramic films. Or, some films can be deposited by chemical vapordeposition as known in the art. Patterning of the films to formmatrices, bands, strips or other designs can be by any suitable etchingchemistry—such as by a chlorine (plasma) etch after deposition andpatterning of a photoresist. It is also possible to deposit and patterna photoresist followed by deposition of the light absorbing material.

[0084] As mentioned elsewhere herein, in each die area (101 in FIG. 15)will be formed an array of micro-mirrors—possibly thousands or millionsof such mirrors in each die area—depending upon the desired resolutionof the image reflected from such micro-mirror array. A frame of lightabsorbing material, such as that disclosed above for surrounding eachdie area, can be provided on the light transmissive substrate tosurround the area where each micro-mirror will be formed on the lighttransmissive substrate. Whereas the frame areas surrounding each die(such as in FIG. 15) are on the order of millimeters to centimeters inlength, the frame areas that surround each micro-mirror are on the orderof microns—depending upon the desired size of the micro-mirrorsformed—e.g. from 5 to 25 microns. Such “micro-mirror frames” areillustrated in FIGS. 14A and 14B as a light absorbing matrix 98 on asubstrate 99—where thousands or millions of such frames illustrated inFIGS. 14A and 14B can be disposed within a single light absorbing frameof FIG. 15. Or course it is not necessary that both micro-mirror framesof FIG. 14 and die frames of FIG. 15 be provided together. The materialsused to form the micro-mirror frames can be those such as set forthabove in relation to die frames and can include an AR coating (the ARcoating can also cover the entire light transmissive substrate ifdesired.

[0085] The “frames” around the micro-mirrors and around the die areas(the micro-mirror array areas) can instead be provided in the form ofstrips or bands—where the light blocking or absorbing material isprovided along some but not all sides of the micro-mirrors (ormicro-mirror arrays). Also, though the light absorbing material ispreferably provided on the same side of the light transmissive substrateas the micro-mirrors, it is also possible to deposit the light absorbingmaterial on the side of the light transmissive substrate opposite fromthe formed micro-mirrors. If the light absorbing material is providedbetween the micro-mirrors and on the same side as the micro-mirrors, itcan be deposited so as to be in the area of impact of the micro-mirrorson the light transmissive substrate. Such impacting of the micro-mirrorson the light transmissive substrate is discussed in detail in U.S. Pat.Nos. 6,356,378, 6,046,840 and 6,172,797 incorporated herein byreference. If the light absorbing strips or frames are disposed at suchimpact point of the micro-mirror, then preferably such material is ahard and at least minimally electrically conductive to allow dissipationof charge that builds up due to repeated impact of the micro-mirrors.

[0086] In the above embodiments, the light absorbing areas are providedon the same substrate as the micro-mirrors. However, it is also possibleto form micro-mirrors on a circuit substrate (e.g. a silicon substratehaving thereon circuitry, electrodes and micro-mirrors). In such a case,the light absorbing layers are provided on a separate light transmissivesubstrate that is held spaced apart from the circuit substrate—thoughpreferably at a small distance such as 75 microns or less, preferably 50microns or less, and more preferably at a closer distance e.g. less than10 microns. It is possible to position the light transmissive substrateat a distance of from 1 to 5 microns. A close relationship between thelight transmissive substrate and the micro-mirrors can allow for betterblocking of light between adjacent micro-mirrors.

[0087] An example of such an arrangement is illustrated in FIG. 17. Ascan be seen in this Figure, a substrate 122 (e.g. a silicon substrate)with circuitry and electrodes thereon (not shown) has formed above thecircuitry and electrodes an array of micro-mirrors 129. In the exampleof FIG. 17, for ease of illustration only a few micro-mirrors are shownalong the length of the mirror array—of course an actual mirror arraywould likely have hundreds or thousands of micro-mirrors along onedimension of the array—depending upon the desired resolution of theprojection display. In the example of FIG. 17, each micro-mirror wouldhave two electrodes disposed on the substrate below for tilting themicro-mirror in opposite directions depending upon which electrodecauses electrostatic attraction of the adjacent micro-mirror. Of courseother arrangements, such as micro-mirrors pivotable towards thesubstrate in a single direction, could be used.

[0088] Substrate 120 is a light transmissive substrate, such as aplastic, glass or quartz substrate—preferably a display grade glasssubstrate. Formed on substrate 120 is a frame 123 that surrounds themicro-mirror array. Frame 123 in many cases will be a frame disposed asa rectangular thin film but it is also possible for a material that actsas a spacer to space the substrates 120 and 122 apart, or as a bondingagent, to be opaque and act as the frame surrounding the micro-mirrorarray. Also disposed on substrate 120 are light absorbing areas 126 thatare disposed between the micro-mirrors 129 when the two substrates aredisposed adjacent each other. Though the light absorbing areas 126 canbe in the form of strips or other patterns, it is preferred that thelight absorbing areas are a grid or matrix that allows light to pass inareas where the micro-mirrors are disposed, but blocks light in areascorresponding to gaps between the micro-mirrors. The materials forforming the light absorbing areas 123 and 126 can be as in the otherembodiments hereinabove. Also, substrates 120 and 122 can be bondeddirectly together or indirectly via packaging or other structure.

[0089] In a preferred embodiment, the substrates are bonded together atthe wafer level by a) bonding e.g. a glass wafer and a silicon wafertogether and then singularizing into dies, or b) bonding glass (or otherlight transmissive material) dies or caps having the light absorbingstrips or grids to a semiconductor (or other circuit containing) waferand then singularizing the semiconductor wafer. It is preferred that thesubstrates 120 and 122 be disposed close to each other (or, if substrate120 is in the form of a concave “cap”, then the area of the cap havingthe matrix be disposed close to substrate 122). Preferably thesubstrates are disposed at a distance of less than 75 microns, and morepreferably less than 50 microns. Or course, closer distances are easilyachieved particularly if the two substrates are bonded together.Substrate distances of 10 microns or less can be achieved, or even 5microns or less if desired.

[0090] Though the light transmissive substrate (e.g. a glass or quartzwafer) can be a window in the micro-mirror package, it is also possibleto bond the light transmissive substrate directly to the semiconductor(silicon substrate with circuitry) at the die or wafer level—preferablyat the die level. In this way, the light transmissive substrate isbonded directly to the semiconductor substrate—allowing a close gapbetween the two substrates. Bonding the two substrates at the waferlevel also allows for protecting the micro-mirrors during wafersingulation into dies—such as set forth in U.S. patent application Ser.No. 10/005,308 to Patel et al. filed Dec. 3, 2001, incorporated hereinby reference.

[0091] Another design for reducing scattering of light and increasingthe contrast ratio is by providing a light absorbing layer or stripalong the edges of the micro-mirrors. The light absorbing material canbe the same as disclosed above with respect to the light absorbingmatrices. As can better be seen in FIG. 16A, a substrate 111 (this canbe a light transmissive substrate such as glass, or a semiconductorsubstrate with actuation circuitry thereon) is provided on which isdeposited a sacrificial layer 112, which can be of any suitable materialsuch as those sacrificial materials disclosed elsewhere herein. Afterdepositing sacrificial layer 112, mirror layer 113 is formed. Mirrorlayer 113 can be a single layer of a reflective material, such as ametal, metal alloy or metal compound, or a laminate of structuralmaterials, where preferably one of the layers is reflective. On layer(s)113 is deposited light absorbing layer 114. Each of the layers in FIG.16A can be patterned prior to depositing the next layer (or patternedtogether with adjacent layers, depending upon the material of theadjacent layers). And, it should be noted that FIGS. 16A and 16B aresimplified views—additional layers such as hinge layers above or belowthe mirror plate 113 (depending upon whether substrate 111 is lighttransmissive or not) would also generally be provided if the hinge isnot formed in the same layer as the mirror plate.

[0092] As can be seen in FIG. 16B, light-absorbing layer 114 isdirectionally etched removing almost all of the light-absorbing layerexcept for strips of light absorbing material 114 a and 114 b alongsides of the mirror plate 113. Once the sacrificial layer 112 is removedas shown in FIG. 16C, a hinged reflective micro-mirror element havingnon-reflective light absorbing edges is formed, pivotably suspendedabove substrate 111. As with the light absorbing matrices, the lightabsorbing mirror edges are preferably dark colored, preferably black.Also, though the light absorbing mirror edges can be formed withdeposition followed by directional etching as mentioned above, use ofphotoresist to selectively deposit the light absorbing material onlyaround the edges of the micro-mirror (or along the edges and “backside”of the micro-mirror), or using photoresist for etching the lightabsorbing layer, can be performed. Many different combinations ofmaterials and deposition and patterning methods can be employed.

[0093] In addition to the edges or sidewalls of the micro-mirror, theperiphery of the reflective surface proximate to the edges or sidewallscan also be coated with light absorbing materials, as shown in FIG. 16D.In this way, scattered light from defects and/or roughness near theedges may thus be reduced, if not eliminated.

[0094] In many operations, the backside surface opposite to thereflective surface for reflecting incident light can also increasescattered light, which scattered light can be collected by theprojection lens or lenses of the projection system, thus reducing thecontrast ratio. To eliminate this scattered light, the backside surfaceof the micro-mirror can then be covered with a light-absorbing layer,for example, layer 114C in FIG. 16E. It is also possible to cover theperiphery of the micromirror surface, the edges or sidewalls and/or theunderside of the micromirror, such as can be seen in FIG. 16F.

[0095] Whether for a situation when the micro-mirror plate and thebackplane wafer with electrodes and control circuitry built thereon areseparate, or whether for a situation where the control circuitry,electrodes and micromirrors are formed on the same substrate,light-absorbing materials can be deposited on the backplane to reducethe scattered light from the backplane, as shown in FIGS. 18A and 18B.Referring to FIG. 18A, electrodes 63 can be covered with light-absorbingmaterials 67. FIG. 18B illustrates that all electrodes are covered withlight-absorbing material 67, however, this is not necessary. Instead,this substrate can be selectively covered with the light-absorbingmaterial as appropriate.

[0096] For example, light-absorbing strips 68 can be deposited in thespaces between adjacent electrodes 63, as shown in FIG. 18B. Thescattered light from these spaces can thus be reduced, if noteliminated. As an optional feature, electrodes and the spaces betweenadjacent electrodes can be selectively covered with light-absorbingmaterials either individually or in combination as appropriate (notshown).

[0097] Preferably, the light transmissive substrate bonded to thesemiconductor substrate (or other substrate having circuitry andelectrodes thereon) hermetically seals the MEMS elements from thesurrounding environment, and preferably at a pressure lower than thesurrounding environment. In order to achieve the lower pressure, the twosubstrates (dies or wafers) are bonded together at subatmosphericpressure and hermetically sealed (followed by wafer singulation ifperformed at the wafer level). Or, the two substrates could be bonded atambient pressure, though not hermetically, followed by a second seal ata lower pressure that hermetically seals off the interior of the bondedsubstrates from the surrounding environment. In one example of such amethod, the two substrates are first bonded with an adhesive (e.g. epoxyor silicone) followed by soldering (this can be application of a solderor solder reflow) or other hermetic seal (e.g. glass frit seal) if theadhesive is insufficiently hermetic. It is also possible to perform bothseals at subatmospheric pressure, or perform such a double seal atambient pressure if it is not desired to have a lower pressure withinthe area between the two substrates. In addition, it may be desirable,whether at lower pressure or not, to seal the two substrates with a gasother than air, such as an inert gas or gases (nitrogen, helium, etc.),or moisture can be added if an anti-stiction agent would better performif some moisture is present in the package. This packaging can also bedesirable for a monolithic MEMS device where both the circuitry and MEMSelements are on the same substrate, as well as where the MEMS elementsare formed on a substrate different from the circuitry.

[0098] If an anti-stiction agent is deposited on the MEMS elements afterrelease, but before bonding the substrates together, it may be desirableto protect the areas that will be required for bonding (e.g. if anadhesive is used—protecting those areas where the adhesive will beapplied), followed by application of the anti-stiction agent, in turnfollowed by removing the protecting agent or film, followed in turn byapplication of the bonding agent. Such a film could be applied in stripsor rings that correspond to the location of the later applied bondingagent, and could be a photoresist or an inorganic thin film applied byCVD or sputtering. In the alternative, the MEMS elements could bereleased, followed by application of an anti-stiction agent. Then, theapplied anti-stiction agent (e.g. a self assembled monolayer formed fromchlorosilane or alkoxysilane precursors) is removed in the areas wherethe bonding agent will be applied (in any pattern—though preferablycircumferentially around the micro-mirror array if the MEMS elements aremicro-mirrors in an array). Removal can be accomplished by laserablation (preferably focusing laser above the substrate), particle beam,application of a stripping chemical (e.g. acetone) or even mechanicalremoval (scoring with a hard or soft object or with a polishing wheel).

[0099] There are many alternatives to the method of the presentinvention. In order to bond the two wafers, epoxy can be applied to theone or both of the upper and lower wafers. In a preferred embodiment,epoxy is applied to both the circumference of the wafer and completelyor substantially surrounding each die/array on the wafer. Spacers can bemixed in the epoxy so as to cause a predetermined amount of separationbetween the wafers after bonding. Such spacers hold together the upperand lower wafers in spaced-apart relation to each other. The spacers actto hold the upper and lower wafers together and at the same time createa space in which the movable mirror elements can move. Alternatively,the spacer layer could comprise walls or protrusions that aremicro-fabricated. Or, one or more wafers could be bonded between theupper and lower wafers and have portions removed (e.g. by etching) inareas corresponding to each mirror array (thereby providing space fordeflection of the movable elements in the array). The portions removedin such intermediate wafers could be removed prior to alignment andbonding between the upper and lower wafers, or, the wafer(s) could beetched once bonded to either the upper or lower wafer. If the spacersare micro-fabricated spacers, they can be formed on the lower wafer,followed by the dispensing of an epoxy, polymer, or other adhesive (e.g.a multi-part epoxy, or a heat or UV-cured adhesive) adjacent to themicro-fabricated spacers. The adhesive and spacers need not beco-located, but could be deposited in different areas on the lowersubstrate wafer. Alternative to glue, a compression bond material couldbe used that would allow for adhesion of the upper and lower wafers.Spacers micro-fabricated on the lower wafer (or the upper wafer) andcould be made of polyimide, SU-8 photo-resist.

[0100] Instead of microfabrication, the spacers could be balls or rodsof a predetermined size that are within the adhesive when the adhesiveis placed on the lower wafer. Spacers provided within the adhesive canbe made of glass or plastic, or even metal so long as the spacers do notinterfere with the electrostatic actuation of the movable element in theupper wafer. Regardless of the type of spacer and method for making andadhering the spacers to the wafers, the spacers are preferably from 1 to250 microns, the size in large part depending upon the size of themovable mirror elements and the desired angle of deflection. Whether themirror arrays are for a projection display device or for opticalswitching, the spacer size in the direction orthogonal to the plane ofthe upper and lower wafers is more preferably from 1 to 100 microns,with some applications benefiting from a size in the range of from 1 to20 microns, or even less than 10 microns.

[0101] Regardless of whether the micro-mirrors and circuitry are formedon the same wafer or on different wafers, when the micro-mirrors arereleased by removal of the sacrificial layer, a sticking force reducingagent can be applied to the micro-mirrors on the wafer to reduceadhesion forces upon contact of the micro-mirrors with another layer orstructure on the same or opposing substrate. Though such adhesionreducing agents are known, in the present invention the agent ispreferably applied to the wafer before wafer bonding (or after waferbonding but before singulation), rather than to the singularized die orpackage for the die. Various adhesion reducing agents, including varioustrichlorosilanes, and other silanes and siloxanes as known in the artfor reducing stiction for micro electromechanical devices, as mentionedelsewhere herein.

[0102] Also, a getter or molecular scavenger can be applied to the waferprior to wafer bonding as mentioned above. The getter can be a moisture,hydrogen, particle or other getter. The getter(s) is applied to thewafer around the released MEMS structures (or around, along or adjacentan array of such structures, e.g. in the case of a micro-mirror array),of course preferably not being in contact with the released structures.If a moisture getter is used, a metal oxide or zeolite can be thematerial utilized for absorbing and binding water (e.g. StayDry SD800,StayDry SD1000, StayDry HiCap2000—each from Cookson Electronics). Or, acombination getter could be used, such as a moisture and particle getter(StayDry GA2000-2) or a hydrogen and moisture getter (StayDry H2-3000).The getter can be applied to either wafer, and if adhesive bonding isthe bonding method, the getter can be applied adjacent the epoxy beadsor strips, preferably between the epoxy and the micromirrors, and can beapplied before or after application of the adhesive (preferably beforeany adhesive is applied to the wafer(s). In one embodiment, a getter (orgetters if more than one type of getter is used) is provided in a trenchor other cavity formed in either (or both) substrates. For example, atrench extending along one or more sides of a micro-mirror array (oraround the entire periphery of the array) could be formed prior todepositing the sacrificial layer and thin films (or at the end before orafter release of the micro-mirrors). Such a trench (or cavity) could beformed in a silicon substrate (e.g. with circuitry and electrodesthereon if formed as the dual substrate approach set forth above, orcircuitry, electrodes and micro-mirrors thereon if formedmonolithically). Or such a trench or cavity for the getter(s) could beformed in the glass substrate. It is also possible to form a trench orcavity in both substrates with the same or different getters depositedtherein.

[0103] In the method of the invention, the first wafer is preferablyglass, borosilicate, tempered glass, quartz or sapphire, or can be alight transmissive wafer of another material. The second wafer can be adielectric or semiconductor wafer, e.g. GaAs or silicon. As noted above,the first and second wafers are bonded together with an adhesive (thoughmetal or anodic bonding are also possible), depending upon the MEMSstructure and the type of micromachining.

[0104] The releasing can be performed by providing any suitable etchant,including an etchant selected from an interhalogen, a noble gasfluoride, a vapor phase acid, or a gas solvent. And, the releasing ispreferably followed by a stiction treatment (e.g. a silane, such as achlorosilane). Also, a getter can be applied to the wafer before orafter the adhesion reducing agent is applied, and before or after anadhesive is applied (if an adhesive bonding method is chosen).Preferably the time from releasing to bonding is less than 12 hours, andpreferably less than 6 hours.

[0105] Specific mirrors and methods for projection displays or opticalswitching could be used with the present invention, such as thosemirrors and methods set forth in U.S. Pat. No. 5,835,256 to Huibersissued Nov. 10, 1998; U.S. Pat. No. 6,046,840 to Huibers issued Apr. 4,2000; U.S. patent application Ser. Nos. 09/767,632 to True et al. filedJan. 22, 2001; Ser. No. 09/564,069 to Richards filed May 3, 2000; Ser.No. 09/617,149 to Huibers et al. filed Jul. 17, 2000; Ser. No.09/631,536 to Huibers et al. filed Aug. 3, 2000; Ser. No. 09/626,780 toHuibers filed Jul. 27, 2000; 60/293,092 to Patel et al. filed May 22,2001; Ser. No. 09/637,479 to Huibers et al. filed Aug. 11, 2000; and60/231,041 to Huibers filed Sep. 8, 2000. Particular mirror shapesdisclosed in U.S. patent application Ser. No. 09/732,445 to Ilkov et al.filed Dec. 7, 2000 could be used. Also, the MEMS device need not be amicro-mirror, but could instead be any MEMS device, including thosedisclosed in the above applications and in application 60/240,552 toHuibers filed Dec. 13, 2000. In addition, the sacrificial materials, andmethods for removing them, could be those disclosed in U.S. patentapplication 60/298,529 to Reid et al. filed Jun. 15, 2001. Lastly,assembly and packaging of the MEMS device could be such as disclosed inU.S. patent application 60/276,222 filed Mar. 15, 2001. Each of thesepatents and applications is incorporated herein by reference.

[0106] The invention has been described in terms of specificembodiments. Nevertheless, persons familiar with the field willappreciate that many variations exist in light of the embodimentsdescribed herein.

We claim:
 1. A method for making a spatial light modulator, comprising:providing a first substrate that is transmissive to visible light;providing a second substrate having an array of circuitry and electrodesthereon; depositing a light absorbing layer on the first substrate toselectively block the passage of light through the first substrate;forming an array of deflectable reflective elements on the first orsecond substrate; and positioning the first and second substratesproximate to each other to form a substrate assembly.
 2. The method ofclaim 1, wherein the positioning of the first and second substratesproximate to each other comprises bonding the first and secondsubstrates together to form the substrate assembly followed bysingulating the substrate assembly into a set of assembly dies, each ofwhich comprises a plurality of deflectable reflective elements.
 3. Themethod of claim 2, wherein the deflectable reflective elementscorrespond to pixels in a direct-view or projection display.
 4. Themethod of claim 1, wherein the light absorbing layer is formed as arectangular frame on the first substrate surrounding the array ofdeflectable reflective elements
 5. The method of claim 4, wherein lightabsorbing material is deposited on the first substrate to further formareas that decrease the amount of light that enters gaps between thedeflectable elements.
 6. The method of claim 1, wherein the lightabsorbing layer is formed as strips, frames or a grid on the firstsubstrate fully or partially surrounding each deflectable element, whenviewed from above, so as to decrease light that enters gaps betweenadjacent deflectable elements.
 7. The method of claim 4, wherein thelight absorbing layer is deposited prior to forming the array ofdeflectable reflective elements and prior to
 8. The method of claim 4,wherein the light absorbing layer is deposited after forming the arrayof deflectable reflective elements.
 9. The method of claim 1, whereinthe light absorbing layer is black.
 10. The method of claim 1, whereinthe light absorbing layer absorbs at least 50% of the light in areaswhere the light absorbing layer is disposed.
 11. The method of claim 10,wherein the light absorbing layer absorbs at least 75% of the light inareas where the light absorbing layer is disposed.
 12. The method ofclaim 11, wherein the light absorbing layer absorbs at least 85% of thelight in areas where the light absorbing layer is disposed.
 13. Themethod of claim 1, wherein the light absorbing layer is a lightabsorbing matrix.
 14. The method of claim 13, wherein the number ofreflective elements in each die is from 6,000 to about 6 million. 15.The method of claim 1, wherein the first substrate is an opticallytransmissive substrate or a substrate having one or more layers thatwhen removed result in an optically transmissive substrate in areasother than in the area of the light absorbing layer.
 16. The method ofclaim 15, wherein the first substrate is glass, borosilicate, temperedglass, quartz or sapphire.
 17. The method of claim 1, wherein the secondsubstrate is a dielectric or semiconductor substrate.
 18. The method ofclaim 17, wherein the second substrate comprises GaAs or silicon. 19.The method of claim 1, wherein the first and second substrates arebonded together with an adhesive.
 20. The method of claim 19, whereinthe adhesive is an epoxy.
 21. The method of claim 20, wherein the epoxycomprises balls or rods of predetermined diameter.
 22. The method ofclaim 1, wherein the substrate assembly is separated into individualdies by scribing and breaking.
 23. The method of claim 1, wherein thesubstrate assembly is tested for abnormalities prior to separation intothe individual dies.
 24. The method of claim 1, further comprisingproviding a spacing substrate between the first and second substrates.25. The method of claim 1, further comprising providing microfabricatedspacers on one or both of the first and second substrates prior tobonding.
 26. The method of claim 19, wherein the adhesive is dispensedby automated controlled liquid dispensing through a syringe.
 27. Themethod of claim 19, wherein the adhesive is dispensed by screen, offsetor roller printing.
 28. The method of claim 26, wherein the syringe ismoved along X-Y coordinates for dispensing.
 29. The method of claim 1,wherein the first and second substrates are aligned prior to bonding,the aligning comprises registration of substrate fiducials on oppositesubstrates.
 30. The method of claim 29, wherein the registration isaccomplished with a video camera having lens magnification.
 31. Themethod of claim 27, wherein the second substrate is a glass or quartzsubstrate.
 32. The method of claim 1, wherein the bonding of thesubstrates comprises the dispensing of a UV or thermal cure epoxy. 33.The method of claim 32, wherein the bonding further comprisesapplication of a force of 10 kg force or more.
 34. The method of claim1, wherein the aligning comprises aligning each deflectable element onthe first substrate with at least one electrode on the second substrate.35. The method of claim 1, wherein the separation of the substrateassembly comprises forming scribes on the first and second substrates.36. The method of claim 35, wherein the scribes are placed in an offsetrelationship to each other in at least one direction.
 37. The method ofclaim 35, wherein the separation further comprises breaking thesubstrate assembly along the scribe lines with a guillotine or fulcrumbreaking machine.
 38. The method of claim 2, further wherein thesingulation of the substrate assembly comprises sawing partially througheach substrate followed by breaking along the sawed lines.
 39. Themethod of claim 38, wherein the sawing is done in the presence of ahigh-pressure jet of water.
 40. The method of claim 1, wherein thebonding comprises applying a sealant near the perimeter of each array onthe substrate.
 41. The method of claim 40, further comprising applying asealant around the perimeter of at least one of the substrates.
 42. Themethod of claim 1, wherein the bonding comprises applying an adhesiveand spacers, the spacers having a size of from 1 to 100 microns.
 43. Themethod of claim 42, wherein the spacers have a size of from 1 to 20microns.
 44. The method of claim 1, wherein the plurality of deflectableelements are reflective mirror elements and are formed on the secondsubstrate which is a light transmissive substrate when in use except inareas of the light absorbing layer.
 45. The method of claim 25, whereinthe microfabricated spacers comprise an organic material.
 46. The methodof claim 42, wherein the spacers are glass or plastic spacers.
 47. Themethod of claim 25, wherein a plurality of microfabricated spacers aredisposed throughout the array of deflectable elements.
 48. The method ofclaim 1, wherein the plurality of deflectable elements are formed on thesecond substrate.
 49. The method of claim 48, wherein the circuitry andplurality of electrodes are formed prior to forming the plurality ofdeflectable elements, wherein the plurality of deflectable elements areformed above the plurality of electrodes on the second substrate. 50.The method of claim 49, wherein a plurality of light absorbing masks areformed on the first substrate.
 51. The method of claim 50, wherein whenthe substrate assembly is singulated into substrate assembly dies, alight absorbing mask is disposed on a first substrate portion withineach substrate assembly die.
 52. The method of claim 1, wherein theplurality of deflectable elements are formed on the first substrate. 53.The method of claim 52, wherein when the first and second substrates arealigned and bonded together, the deflectable elements on the firstsubstrate are each disposed proximate to a corresponding electrode onthe second substrate.
 54. The method of claim 1, further comprisingpackaging the substrate assembly dies.
 55. The method of claim 1,wherein the deflectable elements are micromirrors having jagged orzig-zag edges.
 56. The method of claim 1, further comprising applying astiction reducing agent to one or both substrates before or afterbonding the two substrates together, but before singulating thesubstrate assembly into dies.
 57. The method of claim 1, furthercomprising applying a getter to one or both substrates before bondingthe two substrates together into a substrate assembly.
 58. The method ofclaim 57, wherein the getter is a molecular, hydrogen and/or particlegetter.
 59. The method of claim 57, wherein the getter is a particulateand moisture getter.
 60. The method of claim 57, wherein the getter iscapable of absorbing moisture.
 61. The method of claim 56, wherein thestiction reducing agent is a silane applied to the deflectable elements.62. The method of claim 56, wherein the stiction reducing agent is achlorosilane.
 63. The method of claim 1, further comprising aligning thesubstrates prior to bonding and singulating the bonded substrates intomultiple bonded substrate die portions.
 64. The method of claim 63,wherein the aligning of the substrates has an accuracy of 1 micron orless.
 65. The method of claim 2, further comprising the singulated dieinto a projection system that comprises a light source, a colorsequencer and projection optics.
 66. The method of claim 1, wherein thelight absorbing layer is provided as a grid or matrix on the lighttransmissive substrate.
 67. The method of claim 1, wherein the lightabsorbing layer is provided as strips or bands on the light transmissivesubstrate.
 68. The method of claim 1, wherein the light absorbing layeris black nickel or black chrome.
 69. The method of claim 1, wherein thelight absorbing layer is a black or dark colored metal or metal alloy.70. The method of claim 1, wherein the light absorbing layer is a carboncontaining polymer.
 71. The method of claim 1, wherein the lightabsorbing layer is deposited by sputtering.
 72. The method of claim 1,wherein the light absorbing layer is a carbon containing film.
 73. Themethod of claim 1, wherein the light absorbing layer comprises a carboncompound.
 74. The method of claim 1, wherein the light absorbing layeris a multilayer laminate.
 75. The method of claim 1, wherein the lighttransmissive substrate comprises an AR coating on a surface opposite tothe surface having the light absorbing layer.
 76. The method of claim 1,wherein the light absorbing layer is a light absorbing frame around eachdie area.
 77. The method of claim 1, wherein the light absorbing layeris a light absorbing frame surrounding each micro-mirror.
 78. The methodof claim 1, wherein the light absorbing layer comprises a plurality oflight blocking strips, each of which are proximate to a gap betweenadjacent micromirrors.
 79. The method of claim 76, wherein the lightabsorbing layer is a set of light absorbing frames, each of whichsurrounding a micro-mirror.
 80. The method of claim 79, wherein thelight absorbing frame surrounding each micromirror is on the same sideof the first substrate as the micromirrors.
 81. The method of claim 80,wherein the light absorbing frame is on a side of the first substrateopposite to the side on which the micromirrors are formed.
 82. Themethod of claim 1, wherein the first substrate is bonded to the secondsubstrate at a distance of 75 microns or less from the second substrate.83. The method of claim 82, wherein the first substrate is bonded to thesecond substrate at a distance of less than 10 microns from the secondsubstrate.
 84. The method of claim 83, wherein the first substrate isbonded to the second substrate at a distance of from 1 to 10 micronsfrom the second substrate.
 85. The method of claim 82, wherein the firstsubstrate is a glass or quartz substrate and the second substrate is asilicon substrate and wherein the substrates are bonded together by anorganic or hybrid organic-inorganic adhesive.
 86. A spatial lightmodulator, comprising: a first substrate that is transmissive to visiblelight; a second substrate having an array of circuitry and electrodesthereon; a light absorbing layer on the first substrate disposed toselectively block the passage of light through the first substrate; andan array of deflectable reflective elements on the first or secondsubstrate; wherein the first and second substrates are positionedproximate to each other as a substrate assembly.
 87. The spatial lightmodulator of claim 86, wherein the reflective elements correspond topixels in a direct-view or projection display.
 88. The spatial lightmodulator of claim 86, wherein the light absorbing layer is formed as arectangular frame on the first substrate surrounding the array ofdeflectable reflective elements as viewed from above.
 89. The spatiallight modulator of claim 88, wherein a further light absorbing area isformed as strips, frames or a grid for blocking light between adjacentdeflectable elements.
 90. The spatial light modulator of claim 86,wherein the first and second substrates are bonded together.
 91. Thespatial light modulator of claim 86, wherein the light absorbing layeris black.
 92. The spatial light modulator of claim 86, wherein the lightabsorbing layer absorbs at least 50% of the light in areas where thelight absorbing layer is disposed.
 93. The spatial light modulator ofclaim 92, wherein the light absorbing layer absorbs at least 75% of thelight in areas where the light absorbing layer is disposed.
 94. Thespatial light modulator of claim 93, wherein the light absorbing layerabsorbs at least 85% of the light in areas where the light absorbinglayer is disposed.
 95. The spatial light modulator of claim 86, whereinthe light absorbing layer is a light absorbing matrix.
 96. The spatiallight modulator of claim 95, wherein the number of reflective elementsin a die area is from 6,000 to about 6 million.
 97. The spatial lightmodulator of claim 86, wherein the first substrate is an opticallytransmissive substrate in areas other than in the area of the lightabsorbing layer.
 98. The spatial light modulator of claim 97, whereinthe first substrate is glass, borosilicate, tempered glass, quartz orsapphire.
 99. The spatial light modulator of claim 86, wherein thesecond substrate is a glass or quartz substrate.
 100. The spatial lightmodulator of claim 86, wherein the second substrate is a dielectric orsemiconductor substrate.
 101. The spatial light modulator of claim 100,wherein the second substrate comprises GaAs or silicon.
 102. The spatiallight modulator of claim 86, wherein the first and second substrates arebonded together with an adhesive.
 103. The spatial light modulator ofclaim 86, wherein the second substrate is a glass substrate.
 104. Thespatial light modulator of claim 86, wherein the plurality ofdeflectable elements are reflective mirror elements and are held on thesecond substrate which is a light transmissive substrate.
 105. Thespatial light modulator of claim 86, wherein the plurality ofdeflectable elements are formed on the second substrate.
 106. Thespatial light modulator of claim 105, wherein the circuitry andplurality of electrodes are disposed on the second substrate, whereinthe plurality of deflectable elements are formed spaced above theplurality of electrodes on the second substrate.
 107. The spatial lightmodulator of claim 106, wherein a plurality of light absorbing masks areformed on the first substrate.
 108. The spatial light modulator of claim107, wherein the substrate assembly is a substrate assembly die having alight absorbing mask disposed on a first substrate portion within thesubstrate assembly die.
 109. The spatial light modulator of claim 86,wherein the plurality of deflectable elements are formed on the firstsubstrate.
 110. The spatial light modulator of claim 86, wherein thedeflectable elements are micromirrors having jagged or zig-zag edges.111. The spatial light modulator of claim 86, further comprising astiction reducing agent on one or both substrates.
 112. The spatiallight modulator of claim 86, further comprising a getter on one or bothsubstrates.
 113. The spatial light modulator of claim 112, wherein thegetter is a molecular, hydrogen and/or particle getter.
 114. The spatiallight modulator of claim 112, wherein the getter is a particulate andmoisture getter.
 115. The spatial light modulator of claim 112, whereinthe getter is capable of absorbing moisture.
 116. The spatial lightmodulator of claim 86, wherein the light absorbing layer is provided asstrips or bands on the light transmissive substrate.
 117. The spatiallight modulator of claim 86, wherein the light absorbing layer is blacknickel or black chrome.
 118. The spatial light modulator of claim 86,wherein the light absorbing layer is a black or dark colored metal ormetal alloy.
 119. The spatial light modulator of claim 86, wherein thelight absorbing layer is a carbon containing polymer.
 120. The spatiallight modulator of claim 86, wherein the light absorbing layer isdeposited by sputtering.
 121. The spatial light modulator of claim 86,wherein the light absorbing layer is a carbon containing film.
 122. Thespatial light modulator of claim 86, wherein the light absorbing layercomprises a carbon compound.
 123. The spatial light modulator of claim86, wherein the light absorbing layer is a multilayer laminate.
 124. Thespatial light modulator of claim 86, wherein the light transmissivesubstrate comprises an AR coating on a surface opposite to the surfacehaving the light absorbing layer.
 125. The spatial light modulator ofclaim 86, wherein the light absorbing layer is a light absorbing framearound each die area.
 126. The spatial light modulator of claim 86,wherein the light absorbing layer is a light absorbing frame surroundingeach micro-mirror.
 127. The spatial light modulator of claim 86, whereinthe light absorbing layer comprises light absorbing strips proximate togaps between adjacent micromirrors.
 128. The spatial light modulator ofclaim 125, wherein the light absorbing layer is a light absorbing framesurrounding each micromirror.
 129. The spatial light modulator of claim128, wherein the light absorbing frame surrounding each micromirror ison the same side of the first substrate as the micromirrors.
 130. Thespatial light modulator of claim 129, wherein the light absorbing framesurrounding each die is on a side of the first substrate opposite to theside on which the micromirrors are formed.
 131. The spatial lightmodulator of claim 86, wherein the first substrate is bonded to thesecond substrate at a distance of 75 microns or less from the secondsubstrate.
 132. The spatial light modulator of claim 131, wherein thefirst substrate is bonded to the second substrate at a distance of lessthan 10 microns from the second substrate.
 133. The spatial lightmodulator of claim 132, wherein the first substrate is bonded to thesecond substrate at a distance of from 1 to 10 microns from the secondsubstrate.
 134. A projection system, comprising: a light source; aspatial light modulator for reflecting a beam of light from the lightsource; and projection optics for projecting light reflected off of thespatial light modulator; wherein the spatial light modulator comprises:a first substrate that is transmissive to visible light; a secondsubstrate having an array of circuitry and electrodes thereon; a lightabsorbing layer on the first substrate disposed to selectively block thepassage of light through the first substrate; and an array ofdeflectable reflective elements on the first or second substrate;wherein the first and second substrates are positioned proximate to eachother as a substrate assembly.
 135. The projection system of claim 134,wherein the reflective elements correspond to pixels in a direct-view orprojection display.
 136. The projection system of claim 134, wherein thelight absorbing layer is formed as a rectangular frame on the firstsubstrate surrounding the array of deflectable reflective elements. 137.The projection system of claim 136, further comprising light absorbingmaterial disposed as frames or a grid for absorbing light blocking lightbetween each deflectable element.
 138. The projection system of claim134, wherein the light absorbing layer is formed as a grid on the firstsubstrate surrounding each deflectable element, and as a rectangularframe on the first substrate surrounding the array of deflectablereflective elements.
 139. The projection system of claim 134, whereinthe light absorbing layer is black.
 140. The projection system of claim134, wherein the light absorbing layer absorbs at least 50% of the lightin areas where the light absorbing layer is disposed.
 141. Theprojection system of claim 140, wherein the light absorbing layerabsorbs at least 75% of the light in areas where the light absorbinglayer is disposed.
 142. The projection system of claim 141, wherein thelight absorbing layer absorbs at least 85% of the light in areas wherethe light absorbing layer is disposed.
 143. The projection system ofclaim 134, wherein the light absorbing layer is a light absorbingmatrix.
 144. The projection system of claim 143, wherein the number ofreflective elements in a die area is from 6,000 to about 6 million. 145.The projection system of claim 134, wherein the first substrate is anoptically transmissive substrate in areas other than in the area of thelight absorbing layer.
 146. The projection system of claim 145, whereinthe first substrate is glass, borosilicate, tempered glass, quartz orsapphire.
 147. The projection system of claim 134, wherein the secondsubstrate is a glass or quartz substrate.
 148. The projection system ofclaim 134, wherein the second substrate is a dielectric or semiconductorsubstrate.
 149. The projection system of claim 148, wherein the secondsubstrate comprises GaAs or silicon.
 150. The projection system of claim134, wherein the first and second substrates are bonded together with anadhesive.
 151. The projection system of claim 134, wherein the firstsubstrate is a glass substrate.
 152. The projection system of claim 134,wherein the plurality of deflectable elements are reflective mirrorelements and are held on the second substrate which is a lighttransmissive substrate.
 153. The projection system of claim 134, whereinthe plurality of deflectable elements are formed on the secondsubstrate.
 154. The projection system of claim 153, wherein thecircuitry and plurality of electrodes are disposed on the secondsubstrate, wherein the plurality of deflectable elements are formedspaced above the plurality of electrodes on the second substrate. 155.The projection system of claim 154, wherein a plurality of lightabsorbing masks are formed on the first substrate.
 156. The projectionsystem of claim 155, wherein the substrate assembly is a substrateassembly die having a light absorbing mask disposed on a first substrateportion within the substrate assembly die.
 157. The projection system ofclaim 134, wherein the plurality of deflectable elements are formed onthe first substrate.
 158. The projection system of claim 134, whereinthe deflectable elements are micromirrors having jagged or zig-zagedges.
 159. The projection system of claim 134, further comprising astiction reducing agent on one or both substrates.
 160. The projectionsystem of claim 134, further comprising a getter on one or bothsubstrates.
 161. The projection system of claim 160, wherein the getteris a molecular, hydrogen and/or particle getter.
 162. The projectionsystem of claim 160, wherein the getter is a particulate and moisturegetter.
 163. The projection system of claim 160, wherein the getter iscapable of absorbing moisture.
 164. The projection system of claim 136,wherein the light absorbing layer is provided as strips or bands on thelight transmissive substrate.
 165. The projection system of claim 134,wherein the light absorbing layer is black nickel or black chrome. 166.The projection system of claim 134, wherein the light absorbing layer isa black or dark colored metal or metal alloy.
 167. The projection systemof claim 134, wherein the light absorbing layer is a carbon containingpolymer.
 168. The projection system of claim 134, wherein the lightabsorbing layer is deposited by sputtering.
 169. The projection systemof claim 134, wherein the light absorbing layer is a carbon containingfilm.
 170. The projection system of claim 134, wherein the lightabsorbing layer comprises a carbon compound.
 171. The projection systemof claim 134, wherein the light absorbing layer is a multilayerlaminate.
 172. The projection system of claim 134, wherein the lighttransmissive substrate comprises an AR coating on a surface opposite tothe surface having the light absorbing layer.
 173. The projection systemof claim 134, wherein the light absorbing layer is a light absorbingframe around each die area.
 174. The projection system of claim 134,wherein the light absorbing layer is a light absorbing frame surroundingeach micromirror.
 175. The projection system of claim 134, wherein thelight absorbing layer comprises light absorbing strips proximate to gapsbetween adjacent micromirrors.
 176. The projection system of claim 173,wherein the light absorbing layer is a light absorbing frame surroundingeach micromirror.
 177. The projection system of claim 176, wherein thelight absorbing frame surrounding each micromirror is on the same sideof the first substrate as the micromirrors.
 178. The projection systemof claim 177, wherein the light absorbing frame surrounding each die ison a side of the first substrate opposite to the side on which themicromirrors are formed.
 179. The projection system of claim 134,wherein the first substrate is bonded to the second substrate at adistance of 75 microns or less from the second substrate.
 180. Theprojection system of claim 179, wherein the first substrate is bonded tothe second substrate at a distance of less than 10 microns from thesecond substrate.
 181. The projection system of claim 180, wherein thefirst substrate is bonded to the second substrate at a distance of from1 to 10 microns from the second substrate.
 182. A method for making aspatial light modulator, comprising: providing a first substrate and asecond substrate; forming an array of circuitry and electrodes on thesecond substrate; forming a plurality of strips or frame areas on thefirst substrate to absorb at least 50% of the light incident on thestrips or frame areas; forming an array of deflectable reflectiveelements on the first or second substrate; and bonding the first andsecond substrates together to form a substrate assembly.
 183. A spatiallight modulator, comprising: a first substrate and a second substrate;an array of circuitry and electrodes on the second substrate; an opaquelayer that forms a pattern on the first substrate in order to absorb atleast 50% of the light that is incident on the opaque layer; and anarray of deflectable reflective elements on the first or secondsubstrate; wherein the first and second substrates are positionedproximate to each other as a substrate assembly.
 184. A spatial lightmodulator comprising: a first substrate and a second substrate disposedproximate to each other; circuitry, electrodes and micromirrors formedon the second substrate; and wherein the first substrate is a substratetransmissive to visible light and is disposed at a distance from thefirst substrate of 75 microns or less.
 185. The spatial light modulatorof claim 184, wherein the first substrate is disposed at a distance of50 microns or less from the second substrate.
 186. The spatial lightmodulator of claim 185, wherein the first substrate is disposed at adistance of 10 microns or less from the second substrate.
 187. Thespatial light modulator of claim 184, wherein the first and secondsubstrates are bonded together.
 188. The spatial light modulator ofclaim 187, wherein a light absorbing layer is present on the lighttransmissive substrate and is disposed to selectively block the passageof light through the light transmissive substrate;
 189. The spatiallight modulator of claim 184, wherein the micromirrors correspond topixels in a direct-view or projection display.
 190. The spatial lightmodulator of claim 188, wherein the light absorbing layer is formed as arectangular frame on the first substrate surrounding the array ofdeflectable reflective elements.
 191. The spatial light modulator ofclaim 190, wherein the light absorbing layer is further formed as a gridfor blocking light between each deflectable element.
 192. The spatiallight modulator of claim 188, wherein the light absorbing layer isformed as strips, frames, or a grid on the first substrate surroundingeach deflectable element to decrease light that enters between adjacentdeflectable elements, and as a rectangular frame on the first substratesurrounding the array of deflectable reflective elements.
 193. Thespatial light modulator of claim 188, wherein the light absorbing layeris black.
 194. The spatial light modulator of claim 188, wherein thelight absorbing layer absorbs at least 50% of the light incidentthereon.
 195. The spatial light modulator of claim 194, wherein thelight absorbing layer blocks at least 75% of the light incident thereon.196. The spatial light modulator of claim 195, wherein the lightabsorbing layer blocks at least 85% of the light incident thereon. 197.The spatial light modulator of claim 188, wherein the light absorbinglayer is a light absorbing matrix.
 198. The spatial light modulator ofclaim 197, wherein the number of reflective elements in a die area isfrom 6,000 to about 6 million.
 199. A projection system, comprising: alight source; a spatial light modulator for reflecting a beam of lightfrom the light source; and a series of projection optics for projectinglight reflected off of the spatial light modulator; wherein the spatiallight modulator comprises: a first substrate and a second substratewithin or forming a MEMS package; and an array of circuitry, electrodesand micromirrors on the second substrate; and wherein the firstsubstrate is a substrate transmissive to visible light and is disposedat a distance from the first substrate of 75 microns or less.